1. Field of the Invention
The present invention relates to interdigitated leads-over-chip lead frames and other devices and methods for supporting integrated circuit dice.
2. State of the Art
Integrated circuit (IC) dice or xe2x80x9cchipsxe2x80x9d are small, generally rectangular IC devices cut from a semiconductor wafer, such as a silicon wafer, on which multiple IC""s have been fabricated. Bare IC dice are typically packaged to protect them from corrosion by attaching them to a lead frame for support and heat conduction and then enclosing them in a die package.
Examples of conventional type lead frames having interdigitized lead frame strips and/or lead fingers thereon are illustrated in U.S. Pat. Nos. 4,949,161 and 5,147,815.
A conventional die package 10 including a type of lead frame referred to as a xe2x80x9cLeads-Over-Chipxe2x80x9d (LOC) lead frame 12 is shown in a cut-away view in FIG. 1. The LOC lead frame 12 includes an assembly of conductive leads 14 each having an underside attachment surface adhesively attached to a front-side surface of an IC die 16 using double-sided adhesive tape 18 so the assembly of leads 14 physically supports the IC die 16 within the die package 10. Each conductive lead 14 is wire-bonded to one of a multitude of bond pads on the front-side surface of the IC die 16, and each lead 14 extends from the die package 10 to terminate in a pin that may be connected to external circuitry (not shown) so circuitry within the IC die 16 may communicate with the external circuitry through the bond pads and the conductive leads 14. Of course, while the leads 14 are shown in FIG. 1 as being wire-bonded to bond pads extending along a center axis of the front-side surface of the IC die 16, it will be understood that the leads of an LOC lead frame may also be wire-bonded to bond pads extending about the perimeter of the front-side surface of an IC die.
In another conventional 16 Meg. DRAM semiconductor memory device package for NEC Corporation, a die package 210 including a type of lead frame referred to as a xe2x80x9cLeads-Over-Chipxe2x80x9d (LOC) lead frame 212 is shown in atop view in FIG. 1A. The LOC lead frame 212 includes an assembly of conductive leads 214 each having an underside attachment surface adhesively attached to a front-side surface of an IC die 216 using double-sided adhesive tape (not shown) so the assembly of leads 214 physically supports the IC die 216 within the die package 210. Each conductive lead 214 is wire-bonded to one of a multitude of bond pads on the front-side surface of the IC die 216, and each lead 214 extends from the die package 210 to terminate in a pin that may be connected to external circuitry (not shown) so circuitry within the IC die 216 may communicate with the external circuitry through the bond pads and the conductive leads 214. As shown, the leads 214 in FIG. 1A are wire-bonded to bond pads extending along a single side axis of the front-side surface of the IC die 216.
In yet another conventional 4 Meg.xc3x974 DRAM semiconductor memory device package for NEC Corporation, a die package 310 including a type of lead frame referred to as a xe2x80x9cLeads-Over-Chipxe2x80x9d (LOC) lead frame 312 is shown in a top view in FIG. 1B. The LOC lead frame 312 includes an assembly of conductive leads 314 each having an underside attachment surface adhesively attached to a front-side surface of an IC die 316 using double-sided adhesive tape (not shown) so the assembly of leads 314 physically supports the IC die 316 within the die package 310. Each conductive lead 314 is wire-bonded to one of a multitude of bond pads on the front-side surface of the IC die 316, and each lead 314 extends from the die package 310 to terminate in a pin that may be connected to external circuitry (not shown) so circuitry within the IC die 316 may communicate with the external circuitry through the bond pads and the conductive leads 314. As shown, the leads 314 in FIG. 1B are wire-bonded to bond pads extending along a single side axis of the front-side surface of the IC die 316.
LOC lead frames are well-known in the art, and are described in various embodiments in U.S. Pat. Nos. 4,862,245, 5,218,168, 5,250,840, 5,256,598, 5,381,036, 5,521,426, and 5,563,443.
Conventional LOC lead frames can sometimes be problematic because the arrangement and design of their leads do not allow the leads to cover an optimum percentage of the surface area of an IC die when attached to the die. As a result, the leads are unable to support the die as well as desired, and the leads do not extract as much heat as desired from the die.
In yet another type lead frame configuration, a lead-under-chip type lead frame, illustrated in U.S. Pat. No. 5,360,992, the lead fingers extend under and beyond the semiconductor device acting as a die paddle for the device with wire bonds being formed between the bond pads located on the active surface of the semiconductor device and portions of the lead fingers extending therebeyond. This type of lead frame arrangement requires the use of long lead fingers to extend the length of the semiconductor device and therebeyond for wire bonding purposes thereby affecting the response time of the semiconductor device assembly.
In still yet another type lead frame and integrated circuit package, as illustrated in U.S. Pat. No. 5,585,668, two integrated circuit semiconductor devices are connected to a common substantially planar lead frame, wherein the bond pads on each active surface of a semiconductor device face the common lead frame and are wire bonded to the lead fingers thereof.
Also, it can be difficult to produce die packages having xe2x80x9cmirror imagexe2x80x9d pin-out arrangements using conventional LOC lead frames. A pair of such mirror image die packages has one set of die functions (e.g., VCC, DQ1, DQ2, WE*, RAS*, A10, A0, A1, A2, and A3) associated with the left-side pins of a first one of the pair and the right-side pins of a second one of the pair, and has another set of functions (e.g., VSS, DQ4, DQ3, CAS*, OE*, A9, A8, A7, A6, A5, and A4) associated with the right-side pins of the first one of the pair and the left-side pins of the second one of the pair. Such mirror image die packages can be useful, for example, when a pair of die packages is positioned opposite one another on opposing sides of a Single In-line Memory Module (SIMM) board and shares the same conductors for identical functions. The difficulty in producing a pair of mirror image die packages using conventional LOC lead frames arises because producing the pair traditionally requires: a pair of mirror image dice and identical LOC lead frames, as described in U.S. Pat. Nos. 5,508,565 and 5,530,292; identical dice and a pair of mirror image LOC lead frames, as described in U.S. Pat. No. 5,508,565; or wire-bonding a central row of bond pads on one of the pair of dice to one of an identical pair of LOC lead frames and then reverse-wire-bonding a central row of bond pads on the other of the pair of dice to the other of the pair of LOC lead frames.
Because the traditional methods of producing mirror image die packages using mirror image dice and mirror image LOC lead frames require the production of an additional part, they are inefficient and expensive methods. In addition, using only dice with a central row of bond pads to make mirror image die packages is undesirably restrictive, since many dice have a different arrangement of bond pads.
Therefore, there is a need in the art for an LOC lead frame and other devices and methods for supporting IC dice in an improved manner. Such an LOC lead frame should be capable of producing mirror image die packages, if desired, using identical dice having a wide variety of different bond pad arrangements. The lead frame should also conduct heat away from a die in an improved manner.
An inventive integrated circuit (IC) package includes double-sided adhesive tape overlying and adhesively attached to a front-side surface of an IC die. A Leads-Over-Chip (LOC) lead frame in the package includes a plurality of leads overlying the tape and the front-side surface. An attachment surface of each lead is adhesively attached to the tape, and at least some of the leads extend across the front-side surface of the die from one edge substantially to another edge. As a result, a substantial area of the front-side surface is adhesively attached to the leads through the tape, so the die is supported in the IC package in an improved manner, and heat is conducted away from the die in an improved manner.
In a further embodiment of the present invention, an electronic system includes an input device, an output device, a processor device, and a memory device, and one of the input, output, processor, and memory devices includes the IC package described above.
In another embodiment, an assembly for supporting an IC die includes support members, such as LOC lead frame leads, overlying a front-side surface of the die. An attachment surface of each support member is adhesively attached to the front-side surface, and at least some of the support members extend across the front-side surface from one edge substantially to another edge. As a result, a substantial area of the front-side surface is adhesively attached to the support members.
In a further embodiment, an IC package having a reversible pin-out arrangement includes double-sided adhesive tape overlying and adhesively attached to a front-side surface of an IC die. An LOC lead frame is supported by a package housing and includes a plurality of interdigitated leads overlying the tape and the front-side surface of the die with an attachment surface of each lead adhesively attached to the tape. Each lead in first and second groups of the leads is constructed to extend substantially from respective first and second opposing edges of the front-side surface of the die, across the front-side surface, over the respective second and first opposing edges, away from the die, and out respective first and second opposing sides of the housing to terminate in a pin. Each of a multitude of bond pads on the front-side surface of the die is alternately coupleable to adjacent first and second group leads. As a result, each bond pad is alternately accessible through pins on the first and second opposing sides of the housing, and the IC package thereby has a reversible pin-out arrangement.
In still another embodiment, an electronic device, such as a Single In-line Memory Module (SIMM) board, includes a base, such as a printed circuit board, a first IC package as described above with a first pin-out arrangement, and a second IC package as described above with a second pin-out arrangement that mirrors the first pin-out arrangement.
In a still further embodiment, an IC quad-package having a reversible pin-out arrangement includes double-sided adhesive tape overlying and adhesively attached to a front-side surface of an IC die. An LOC lead frame is supported by a package housing and includes a plurality of interdigitated leads overlying the tape and the front-side surface of the die with an attachment surface of each lead adhesively attached to the tape. Each lead in first, second, third, and fourth groups of the leads is constructed to extend substantially from respective first and second adjacent edges and third and fourth adjacent edges of the front-side surface of the die, across the front-side surface, over the respective second, first, fourth, and third edges, away from the die, and out respective first and second adjacent sides and third and fourth adjacent sides of the housing to terminate in a pin. Each of a first group of bond pads on the front-side surface of the die is alternately coupleable to adjacent first and second group leads, and each of a second group of bond pads on the front-side surface of the die is alternately coupleable to adjacent third and fourth group leads. As a result, each bond pad in the first group is alternately accessible through pins on the first and second adjacent sides of the housing, each bond pad in the second group is alternately accessible rough pins on the third and fourth adjacent sides of the housing, and the IC quad-package thereby has a reversible pin-out arrangement.
In still another embodiment, an electronic device, such as a Single In-line Memory Module (SIMM) board, includes a base, such as a printed circuit board, a first IC package as described above with a first pin-out arrangement, and a second IC package as described above with a second pin-out arrangement that mirrors the first pin-out arrangement.
In an additional embodiment, a method for supporting an IC die in an IC package includes: positioning the die in proximity to a housing of the package; supporting a multitude of support members on the housing; and maintaining the position of the die in proximity to the housing by adhesively attaching an attachment surface of each support member to a front-side surface of the die and by extending at least some of the support members across the front-side surface in adhesive attachment with the surface from one edge substantially to another edge so a substantial area of the surface is adhesively attached to the support members.